RS485 wired communication
Most early PV plants use RS485 communication, which is used for communication between the combiner boxes, inverters, box-type transformers, and EMI in the subarray. The transmission rate is 9600bps, and the maximum transmission rate is 19.2Kbps.
RS485 is a wired communication mode and requires dedicated communications cables. During the construction of a power station, trenches must be buried and cables must be laid out. Otherwise, the communication quality will be affected. Therefore, many problems are frequently encountered in the application of the RS485 project. For example: The RS485 combiner box is incorrectly connected because the construction personnel are not professional. During the construction, the cables that have been laid out are broken, causing secondary faults. After the RS485 is laid, dedicated personnel are required to maintain the line, which increases the investment cost of the project.
In addition, RS485 communication has the following characteristics: Cables are mutually exclusive. Once a cable is faulty, the system cannot accurately locate the fault segment. In this case, you can only re-search for rework. The repeated burial of cables greatly increases the labor cost. At the same time, if the construction personnel are not professional enough, they will bury new hidden troubles, causing the fault to recur.
Power carrier communication (PLC)
With the continuous development of the PV industry and the continuous acceleration of PV plant construction, the initial RS485 cannot meet the requirements of the industry. The new-generation communication technology, Power Line Communication (PLC), emerges.
PLC is a kind of communication mode that uses power line to transmit data signal. Compared with RS485, RS485 has the following advantages: 1. The AC power cable is used as the channel. As long as the cable is continuous, the communication is not interrupted, and no RS485 cable or construction project is required. 2. The delivery period is short, the delivery cost is low, and the maintainability is good.
However, the disadvantage of this communication mode is that the PLC application scope of some manufacturers is narrow, and only the 9kHz~490kHzp frequency band is supported. The transmission rate is low, less than 5kbps, and the transmission delay is 150 ms. The number of subcarriers is small, the anti-interference capability is weak, and the reliability is low. The low-voltage grid connection is not supported.
MBUS communication
With the development of communication technologies and Internet of Things (IoT) technologies in China, a new communication mode is emerging. This is the MBUS communication solution. This technology does not require additional RS485 communications cables, which shortens the construction period and reduces investment and O&M costs.
The MBUS inherits all advantages of the PLC and innovatively upgrades the PLC. The transmission rate is faster, the transmission delay is shorter, and the anti-interference capability is stronger. The new architecture and Lite OS operating system are used to carry Huawei's new-generation HiSilicon chip. The anti-interference capability is improved by 10 times, the 0.5 MHz ~ 12 MHz wider frequency band is supported, the actual transmission rate is 115kbps, and the transmission delay is less than 30 ms. This meets the requirements for fast response to power grid scheduling and supports low-voltage grid-tied scenarios.
The MBUS communication solution integrates information transmission rate, small transmission delay, better support for power grid scheduling, and lays a solid foundation for future intelligent upgrade of power grids. It is being accepted by more and more power plant owners. It is understood that a 100MW PV plant in the Changzhi runner base uses the Huawei MBUS communication solution, which is highly appraised by the owner.
